1. Field of the Invention
This invention generally relates to a method of manufacturing a worked-wire product, a manufacturing apparatus therefor, and a resultant worked-wire product.
2. Related Background Art
Recently, notebook-sized personal computers have increasingly commanded a considerable share of the computer market. In addition to that fact, so-called mobile computers are becoming pervasive as mobile communication terminals or gears. Thus, the computers are increasingly required to be made more compact and lightweight.
Furthermore, such as an operation speed in computers including the personal computers becomes more and more fast. This inevitably requires parts or elements of the computers to be more densely packed. Under such circumstances, not only flat or ribbon cables each comprising multiple core wires are favorably employed in the computers, but also flat cables are increasingly required to be installed in a limited space. Moreover, it becomes more earnestly desired to obtain matching of characteristic impedance at a higher accuracy than that heretofore possible.
In order to meet with such requirements, it has been required that during connecting operation of flat multi-core cable, the outer conductor of each wire comprising the associated cable is grounded certainly and the core conductor thereof be securely connected to connection points arrayed at a predetermined pitch in a connector terminal or a substrate.
Japanese Laid-Open Patent Publication No. 10-144145 discloses a worked-wire product in the form of a flat cable comprising a multiplicity of extra-fine core a wires and a method of manufacturing the same. According to this disclosed method, a length of each outer conductor is cut off by repetitions of mechanical bending thereof in order to expose the end of the associated core conductor, with the intention of effectively performing the cable connecting operation.
The inventors have applied themselves closely to the study of the above prior art. As a result, they have found that the prior art involves the following drawbacks, that is:
(1) Simultaneously with the repetitive bending of the outer conductors, the core conductors are also subject to a bending motion so that a bending induced deflection or strain (bending strain) may be progressively build up at the bend of the core conductor. In the case where the core conductor consists of a single wire, this may cause a so-called xe2x80x9cthinnedxe2x80x9d area to be developed at the bend of the core conductor, resulting in a decrease in breaking force (load) of the core conductor thereat and an incomplete contact of the core conductor to a connector terminal, which in turn may eventually result in the break of the core conductor.
(2) In the case where the core conductor comprises a stranded wire or wires, some elementary wires forming the stranded wire may fray. As a result, a so-called xe2x80x9cbarb(s)xe2x80x9d may appear. This disadvantageously affects work efficiency in connecting the raveled conductor to the connector terminal and so on. According to the circumstances, the incomplete contact of the core conductor to the connector terminal may be occur. This results that certain worked-wire products may be rejected on inspection, reducing yields.
It is to be noted that the term xe2x80x9cthinnedxe2x80x9d used herein means such a condition that the size concerned reduces in diameter by e.g. 5% relative to that of a straight portion and may be subject to stress concentration. When the core conductor encounters such a reduction in diameter, its cross section may be decrease. Therefore, the core conductor is lessened in breaking force so that it becomes embrittled. It is to be noted that the term xe2x80x9cbarbxe2x80x9d used herein represents an elementary wire projection, which separately extends from the end portion of other elementary wires comprising the stranded wire.
The present invention has been made in view of the above circumstances and has for its object to provide a method of manufacturing a worked-wire product, a manufacturing apparatus therefor, and a resultant worked-wire product, in which when a core conductor comprising wires is repeatedly bent to cause the end portion of the core conductor to be exposed, it is possible to prevent the occurrence of a decrease in core conductor strength and of broken core conductor.
The inventors have repeated diligent studies in order to achieve the above-mentioned object, and have found that, there is a close connection between wire bending modes and changes in mechanical strength of a core conductor at a bend, whereby the present invention is accomplished.
According to one aspect of the invention, a method of manufacturing a worked-wire product is provided, which comprises the steps of: providing a wire including a core conductor, an insulator surrounding the core conductor, an outer conductor surrounding the insulator, and a sheath surrounding the outer conductor; exposing a portion of the outer conductor; holding the exposed portion of the outer conductor at least at two positions by at least two holders; bending the outer conductor until it is circumferentially cut off, the bending being effected by a repeated bending motion (oscillating motion) of at least one of the holders about a bending center (or a fulcrum) present between adjacent holders while applying ultrasonic vibrations on the outer conductor through at least one of the holders; removing the cut off portion of said outer conductor to expose a portion of the insulator; and removing the exposed portion of the insulator to expose a portion of the core conductor.
According to such a method of manufacturing a worked-wire product, the ultrasonic vibrations applied on the outer conductor simultaneous with the bending thereof accelerate the deformation of the outer conductor at the bend thereof. This causes a crack or cracks to be easily created in the bend, so that the outer conductor can be readily cut off as compared with the prior art. It is assumed that the readiness of cut can be derived from interaction between the repeated bending and the fine and high-speed (i.e., short repetition cycle) mechanical movement of the bend of the outer conductor due to the ultrasonic vibrations.
Furthermore, the outer conductor can be readily and securely cut off, even if it is repeatedly bent at an angle smaller than that has been carried out in the prior art. Accordingly, it is possible to prevent the core conductor from being excessively bent, unfavorably resulting in the strain being stored in the core conductor. Thus, the occurrence of not only the xe2x80x9cthinnedxe2x80x9d bend of the core conductor consisting of a single wire, but also the so-called xe2x80x9cbarbxe2x80x9d in the stranded wire of the core conductor, which have been occurred in the prior art, can be considerably decreased.
Preferably, the bending of the outer conductor is effected so that the outer conductor is bent about the bending center (i.e., about an inflection point) at an angle of below 30xc2x0, more preferably 10xc2x0 or less, from a longitudinal axis of the wire.
If the angle of bending reaches 30xc2x0 or more, there occurs a clear tendency that a relatively large amount of strain is stored in the bend of the core conductor until the outer conductor is cut off. Thus, it is understood that, by setting the angle of bending below 30xc2x0, the occurrence of not only the xe2x80x9cthinnedxe2x80x9d bend of the core conductor, but also the so-called xe2x80x9cbarbxe2x80x9d in the core conductor comprising the stranded wire, which have been occurred in the prior art, can be further decreased.
Furthermore, if the angle of bending is set to 10xc2x0 or less, the occurrence of such xe2x80x9cthinnerxe2x80x9d bend and xe2x80x9cbarbxe2x80x9d can be prevented more effectively. As stated above, with the method of manufacturing the worked-wire product according to the invention, the outer conductor is bent while being subject to the ultrasonic vibrations so that the outer conductor alone can be readily cut as compared with the prior art. Thus, if the angle of bending is set below 30xc2x0, it is possible to shorten a period of time necessary to cut off the outer conductor as compared with the prior art. As a result, an improvement in workability can be realized.
According to another aspect of the invention, a manufacturing apparatus for advantageously embodying the method of manufacturing a worked-wire product according to the invention is provided. The apparatus manufactures the worked-wire product from a wire including a core conductor, an insulator surrounding the core conductor, an outer conductor surrounding the insulator, and a sheath surrounding the outer conductor. The apparatus comprises at least two holders holding an exposed portion of the outer conductor at least at two positions, respectively; and a vibration exciter applying ultrasonic vibrations on the outer conductor through at least one of the holders.
It is preferable that the apparatus further comprises a device for bending the outer conductor through a repeated bending (oscillating) motion of at least one of the holders about or around a bending center present between adjacent holders, i.e., about the bending center as a center point of rotatory motion of the holder(s).
According to further aspect of the invention, a worked-wire product is provided, which includes a core conductor, an insulator surrounding the core conductor, an outer conductor surrounding the insulator, and a sheath surrounding the outer conductor, the core conductor being partially exposed using a manufacturing method according to the present invention.
It is understood that ultrasonic waves available in the present invention are sonic or acoustic waves including elastic waves having a frequency of 20 kHz or more. The frequency and/or intensity may be constant or changed regularly or irregularly. The ultrasonic wave may include a frequency component within an audio-frequency range.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.